U.S. patent application number 12/304792 was filed with the patent office on 2010-03-11 for cell selection/reselection mechanism for a mobile communication system.
Invention is credited to Magnus Hallenstal, Tomas Nylander, Jari Vikberg.
Application Number | 20100061337 12/304792 |
Document ID | / |
Family ID | 37761936 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100061337 |
Kind Code |
A1 |
Hallenstal; Magnus ; et
al. |
March 11, 2010 |
Cell Selection/Reselection Mechanism for a Mobile Communication
System
Abstract
A method and mobile station for operating within one or more
radio access networks. The radio access network broadcasts system
information messages which indicate whether the network or cell
supports a packet-switched handover procedure. The mobile station
receives the system information messages and utilizes the indicated
support as a factor in selecting a cell or routing area of a radio
access network within which to camp.
Inventors: |
Hallenstal; Magnus; (Taby,
SE) ; Vikberg; Jari; (Jarna, SE) ; Nylander;
Tomas; (Varmdo, SE) |
Correspondence
Address: |
ERICSSON INC.
6300 LEGACY DRIVE, M/S EVR 1-C-11
PLANO
TX
75024
US
|
Family ID: |
37761936 |
Appl. No.: |
12/304792 |
Filed: |
June 16, 2006 |
PCT Filed: |
June 16, 2006 |
PCT NO: |
PCT/EP2006/063301 |
371 Date: |
June 12, 2009 |
Current U.S.
Class: |
370/331 ;
455/436 |
Current CPC
Class: |
H04W 36/14 20130101;
H04W 48/20 20130101 |
Class at
Publication: |
370/331 ;
455/436 |
International
Class: |
H04W 36/14 20090101
H04W036/14; H04W 48/20 20090101 H04W048/20 |
Claims
1-12. (canceled)
13. A method of operating a mobile station within one or more radio
access networks, the method comprising: receiving in the mobile
station, system information messages broadcast by a radio access
network, the system information messages including an indication of
whether the broadcasting network provides support for a packet
switched handover procedure; and using the indication of support
for packet switched handover as a factor in selecting by the mobile
station, a cell of a radio access network/technology or a Routing
Area of a radio access network within which to camp.
14. The method according to claim 13, wherein the radio access
networks employ one of the following technologies: General Packet
Radio Service (GPRS), Universal Mobile Telecommunications System
(UMTS), and Long Term Evolution (LTE).
15. The method according to claim 13, wherein the system
information messages indicate support for a packet switched
handover procedure at the cell level, the Routing Area level, the
radio access network/technology level, or the mobile network
level.
16. The method according to claim 13, further comprising the mobile
station selecting to camp in a cell of a radio access network that
supports packet switched handover.
17. The method according to claim 13, further comprising the mobile
station analyzing the broadcast information to determine the
suitability of the cells taking into consideration information
stored in the mobile station regarding a likely use of the mobile
station.
18. The method according to claim 13, wherein the mobile station is
operating in idle mode.
19. A mobile station for use within one or more radio access
networks, the mobile station comprising: means for receiving system
information messages broadcast by a radio access network, the
system information messages including an indication of whether the
broadcasting network provides support for a packet switched
handover procedure; and means for using the indication of support
for packet switched handover as a factor in selecting by the mobile
station, a cell of a radio access network/technology or a Routing
Area of a radio access network within which to camp.
20. A radio access network comprising: means for determining
whether the radio access network supports a packet switched
handover procedure; and means for causing an indication of support
for the packet switched handover procedure to be broadcast within
the radio access network, upon determining that the radio access
network supports the packet switched handover procedure.
21. The radio access network according to claim 20, wherein the
indication of support for the packet switched handover procedure is
an indication of support for performing a packet switched handover
within a cell or Routing Area, or across the entire radio access
network.
22. The radio access network according to claim 20, wherein the
information broadcast about the capabilities of the cells comprises
at least one of the following: Quality of Service supported; types
of traffic supported; peak throughput for the Quality of Service
supported; peak throughput for the types of traffic supported; and
an indication of standardized profiles supported.
23. The radio access network according to claim 20, wherein the
means for causing an indication of support for the packet switched
handover procedure to be broadcast includes one of a Radio Network
Controller of a Universal Mobile Telecommunications System (UMTS)
radio access network, a Base Station Controller of a Global System
for Mobile Communications (GSM) access network, and an appropriate
node of a Long Term Evolution (LTE)-based network.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a cell selection/reselection
mechanism for a mobile communication system. In particular, the
invention relates to a method and apparatus for enabling a mobile
station (MS)--or user equipment (UE) in 3G parlance--to select a
cell in which to camp in idle mode, in order to receive the most
appropriate service support upon session activation.
BACKGROUND TO THE INVENTION
[0002] IP Multimedia (IPMM) is an example of a service which
provides a dynamic combination of voice, video, messaging, data,
etc, within the same session. By growing the numbers of basic
applications and the media which it is possible to combine, the
number of services offered to the end users will grow, and the
inter-personal communication experience will be enriched. This will
lead to a new generation of personalized, rich multimedia
communication services, e.g. peer-to-peer multimedia communication,
IPTV etc.
[0003] These services can be based on the IP Multimedia Subsystem
(IMS) architecture, which is the technology defined by the Third
Generation Partnership Project (3GPP) to provide IP Multimedia
services over mobile communication networks (3GPP TS 22.228, TS
23.228, TS 24.229, TS 29.228, TS 29.229, TS 29.328 and TS 29.329
Releases 5 to 7). The IMS makes use of the Session Initiation
Protocol (SIP) to set up and control calls or sessions between user
terminals (or user terminals and application servers). The Session
Description Protocol (SDP), carried by SIP signalling, is used to
describe and negotiate the media components of the session. Other
multimedia applications which can be used for media transmission
and control include Real-time Transport Protocol and Real-time
Transport Control Protocol (RTP/RTCP), Message Session Relay
Protocol (MSRP), and Hyper Text Transfer Protocol (HTTP).
[0004] FIG. 1 illustrates schematically how the IMS fits into the
mobile network architecture in the case of a 3GPP PS access
network. Call/Session Control Functions (CSCFs) operate as SIP
proxies with the IMS. The 3GPP architecture defines three types of
CSCFs: the Proxy CSCF (P-CSCF) which is the first point of contact
within the IMS for a SIP terminal; the Serving CSCF (S-CSCF) which
provides services to the user that the user is subscribed to; and
the Interrogating CSCF (I-CSCF) whose role is to identify the
correct S-CSCF and to forward to that S-CSCF a request received
from a SIP terminal via a P-CSCF.
[0005] A fundamental requirement for real-time service provision is
the seamless handover of services for subscribers roaming across
cell boundaries of the radio access network (RAN) or subscribers
roaming across RAN or radio access technology (RAT) boundaries
(e.g. moving between 2G, 3G and/or LTE networks). Traditional
circuit switched (CS) based call services have been designed to
meet this requirement. In the case of 2G and currently implemented
3G networks, PS real time handover with low latency is not provided
for, although service continuity is achieved at the terminal side
by ordering a session to be moved from one cell to the other, i.e.
there is no prepare phase to shorten latency when moving cell. Real
time PS handover is standardized in 3GPP for 3G networks, but the
feature has not yet been deployed. It is expected that when
High-Speed Downlink Packet Access (HSDPA) is deployed, or shortly
thereafter, the mechanisms needed for fast PS handover will also be
deployed. For 2G networks, fast and efficient PS handover
procedures in the packet switched (PS) domain have only recently
been standardized in 3GPP TS 43.129, and in the initial
implementation stage, roll-out of this feature across 3G networks
will inevitably be patchy. In addition, support for PS handover in
2G networks such as GSM/GPRS networks is never likely to be
comprehensive (if implemented at all), yet handover of PS calls
would be desirable as 2G networks will continue to provide a
fallback network for 3G subscribers in the case of limited 3G
network coverage. It can also expected that the next generation
radio and core networks which are currently being specified under
the name LTE (Long Term Evolution) and SAE (System Architecture
Evolution) in 3GPP will also have limited coverage, and that these
networks will also require fallback to 3G and 2G networks.
[0006] It is expected that in the future all peer-to-peer
multimedia communications in the mobile network will run over the
PS domain. In particular, as voice calls are just a special variant
of peer-to-peer multimedia communication, all voice calls will be
Voice-over-IP (VoIP) calls. VoIP calls will be particularly
sensitive to even relatively minor service interruptions caused by
inter-cell handovers. As long as a terminal engaged in a VoIP call
can perform PS handover to another cell (the "target cell"), the
interruption can be kept short enough to avoid any noticeable drop
in perceived quality. However, if either the current cell or the
target cell do not support PS handover, a noticeable interruption
is likely to occur as packets will be lost or delayed during the
transition period. Consequently, until all RAN cells support PS
handover, the provision of IMS services such as voice and video
calls utilising the PS domain is likely to result in users
receiving a reduced quality of service when crossing cell
boundaries.
[0007] International patent application number PCT/EP04/05333
describes a process for allowing the IMS to automatically establish
a VoIP call over a CS network when a user requests the VoIP call
using signalling sent over a PS network. In this way, the IMS
ensures that the appropriate Quality of Service (QoS) is applied to
the call. In addition, the VoIP CS call will benefit from the
seamless handovers afforded by the CS domain, if and when the user
moves into a neighbouring cell. The procedure involves the
establishment of a CS leg between the IMS and the Mobile Switching
Centre (MSC) in order to link the CS access network leg to the IMS.
This is achieved using an inter MSC handover procedure.
[0008] The disadvantage associated with the above proposal is that
a VoIP call is automatically carried over the CS network even if
the PS network is able to provide a satisfactory QoS for the VoIP
call. In addition, the process of transferring the call to the CS
network will consume significant resources within the network and,
where the PS network can support the call, this will be wasted
effort. Moreover, the above proposal is concerned with the
establishment of a VoIP call in the cell in which the mobile
station (MS) has selected, based on measured signal strength,
regardless of the PS handover capabilities of that particular
cell.
[0009] In the PS domain, a MS can generally be said to be in one of
three different mobility management states. For UMTS these are:
[0010] PMM-DETACHED State [0011] Here the MS (or its location) is
not known to the network and it has no IP address, i.e. it has not
"logged on" to the PS domain; [0012] PMM-IDLE State [0013] The MS
has "logged on" to the PS domain and it has an IP address, but it
is not engaged in a session/call. The network knows which Routing
Area the MS is in, but not the specific cell within that Routing
Area. [A Routing Area comprises a set of cells under which the
system can page a MS if it wants to start a session.] Typically,
all of the cells within a Routing Area will share the same
capabilities. It is the role of the MS to decide the most
appropriate cell and thus Routing Area for it to camp on. Once
camped within a chosen cell, the MS will select, based upon
measured signal strength, and chooses a particular cell over which
to send Routing Area updates (as needed) to the network and over
which to initiate calls/sessions; and [0014] PMM-CONNECTED State
[0015] The MS location is known by the network.
[0016] The corresponding states in GPRS are: IDLE state, STANDBY
state and READY state.
[0017] When the MS is in PMM-IDLE state or STANDBY state, as well
as selecting a cell to camp on, it can also select which Radio
Access Technology (RAT) to camp on, WCDMA or GPRS, depending on MS
preferences. When LTE (Long Term Evolution) networks are
introduced, yet another RAT will be available. For the sake of
simplicity in this document, UMTS PMM-IDLE state and GPRS STANDBY
state and corresponding LTE/SAE state will be denoted as the MS
being in idle mode
SUMMARY OF THE INVENTION
[0018] According to the state of the art, the MS itself has no
knowledge of the packet switched handover capabilities of any
particular cell (or Routing Area) or RAT and therefore is not able
to take this factor into account when selecting a cell (and Routing
Area) or RAT within which to camp. This means that a MS that is
capable of VoIP in the PS domain may be camped unknowingly in a
cell of a Routing Area or RAT that does not support PS handover,
even though another available cell (and Routing Area) or RAT does
have this capability.
[0019] According to a first aspect of the present invention there
is provided a method of operating a mobile station within one or
more radio access networks, the method comprising: [0020] receiving
system information messages broadcast by a radio access network,
these messages indicating support within the broadcasting network
for a packet switched handover procedure; and [0021] using the
indicated support for packet switched handover as a factor in
selecting a cell of a radio access network/technology and/or a
Routing Area of a radio access network within which to camp.
[0022] The invention is applicable in particular to mobile stations
operating in an idle mode.
[0023] Where a plurality of radio access networks/radio access
technologies are available to the mobile station, these
networks/technologies may employ the same or different radio access
technologies. Radio access technologies include; GPRS, UMTS, and
LTE. Of course, a single radio access network may make available
two or more radio access network technologies, e.g. UMTS and LTE,
in which case a mobile station may choose one of the available
technologies on which to camp.
[0024] Said system information messages may indicate support for a
packet switched handover procedure at the cell level, the Routing
Area level, or across the whole radio access network of an
operator.
[0025] Embodiments of the invention allow the mobile station to
choose to camp in a cell of a Routing Area and optionally radio
access network/technology that is most suitable for supporting the
types of sessions/calls that it is likely to be used for.
Consequently, a mobile station that is capable of VoIP can select a
cell (or Routing Area) and radio access technology that supports PS
handover, thus ensuring that if and when a VoIP call is established
in a particular cell within the Routing Area and radio access
network/technology, there is at least a possibility that the call
can be handed over to a PS bearer in a neighbouring cell (actual
handover will of course depend upon the neighbouring cell also
supporting PS handover). As all cells within a Routing Area are
likely to have the same capabilities, the chances of the
neighbouring cell also supporting PS handover are increased if both
cells are within the same Routing Area.
[0026] Conveniently, a field indicating support for PS handover is
broadcast where applicable. The absence of this field may be taken
by the mobile station to indicate a lack of support for PS handover
by the sending cell.
[0027] Optionally, a field indicating support for PS handover
across an entire network/technology is broadcast where applicable.
Similarly to the above, the absence of this field may be taken by
the mobile station to indicate that the radio access network of the
broadcasting cell does not support PS handover across all of its
cells.
[0028] In another embodiment of the invention, the information
broadcast about the capabilities of the cells comprises one or more
of the following: [0029] The Quality of Service supported; [0030]
The types of traffic supported; [0031] The peak throughput for the
Quality of Service supported; [0032] The peak throughput for the
types of traffic supported; [0033] Current traffic load; and [0034]
An indication of standardised profiles which are supported.
[0035] Optionally, the mobile station analyses the broadcast
information to determine the suitability of the cells taking into
consideration information stored in the mobile station regarding
the likely use of the mobile station.
[0036] According to a second aspect of the present invention there
is provided a mobile station for use within one or more radio
access networks, the mobile station comprising: [0037] means for
receiving system information messages broadcast by a radio access
network, these messages indicating support within the broadcasting
network for a packet switched handover procedure; and [0038] means
for using the indicated support for packet switched handover as a
factor in selecting a cell of a radio access network/technology
within which to camp.
[0039] According to a third aspect of the present invention there
is provided a radio access network comprising: [0040] means for
broadcasting an indication of support within the radio access
network for a packet switched handover procedure.
[0041] In a particular embodiment of the third aspect of the
invention, the indication of support within the radio access
network is an indication of support for a packet switched handover
within a cell or Routing Area, and/or across the entire
network.
[0042] According to a fourth aspect of the present invention there
is provided apparatus comprising means for causing an indication of
support, within a cell, Routing Area and/or radio access network,
for a packet switched handover procedure, to be broadcast to
listening mobile stations.
[0043] The apparatus of the fourth aspect of the present invention
may be a Radio Network Controller of a UMTS radio access network, a
Base Station Controller of a GSM access network, or an appropriate
node of a LTE-based network.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 illustrates schematically the integration of an IP
Multimedia Subsystem into a 3G mobile communications system;
and
[0045] FIG. 2 illustrates the relationship and interfaces between
multiple radio access networks, circuit switched and packet
switched core networks, and a service network; and
[0046] FIG. 3 illustrates schematically three overlaid radio access
networks having respective different radio access network
technologies.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0047] With reference to FIG. 2, there is illustrated a mobile
station (MS) which may be attached to one of three radio access
networks (RANs). The upper two RANs shown in the Figure support
packet switched (PS) handover while the lower RAN only supports
circuit switched (CS) handover. For the purpose of this discussion,
the upper RAN is assumed to be a LTE based network, the middle RAN
is assumed to be a UMTS Terrestrial RAN (UTRAN) comprising a Radio
Network Controller (RNC) that will allocate transmission bandwidth
to subscribers, and the lower RAN is assumed to be a GSM/GPRS RAN
comprising a Base Station Controller (BNC) that will allocate
transmission bandwidth to subscribers.
[0048] Within the 3GPP 2G and 3G PS core network, PS services are
facilitated by a Serving GPRS Support Node (SGSN) and a Gateway
GPRS Support Node (GGSN). [In 3GPP SAE/LTE the current standard's
view is that the PS service will be facilitated by a so-called aGW
(access GateWay).] For the 2G and 3G cases, the GGSN is coupled to
the IMS core network. In order to access the IMS, the MS must first
register with the IMS using the Session Initiation Protocol (SIP)
REGISTER message. To establish and control an IMS service, the MS
exchanges further SIP messages with the S-CSCF. SIP messages are
transported via a physical PS transport channel. Within the IMS,
the P-CSCF is responsible for requesting and releasing PS network
resources at the GGSN.
[0049] The present proposal aims to enable a mobile station (MS)
operating in idle mode to select a cell of a Routing Area and/or
Radio Access Technology in which to camp. As already described
above, a Routing Area comprises a set of cells under which the
network can page the MS. The Radio Access Technology is the
technology used on the radio interface between the base station and
the MS, e.g. CDMA, TDMA, OFDM etc. The MS is able to make an
informed selection based upon a knowledge of the capabilities of
the cells, Routing Areas or RATs within RANs. Thus, a MS can select
to camp in a cell of a Routing Area and/or RAT that is most
suitable for supporting the types of sessions/calls that are likely
to be activated. By way of example, if VoIP is likely to be
employed, the MS can preferentially select a Routing Area and/or
RAT that supports PS handover. This reduces the risk of a VoIP call
being initiated over a PS bearer within a cell from which handover
of the call to a PS bearer within a neighbouring cell is not
possible.
[0050] In order to implement the present invention, it is necessary
that information regarding the capabilities of cells, Routing Areas
and RATs be broadcast to listening MSs. In the case of a 2G
network, this information may be incorporated into the System
Information messages that are broadcast in a cell of a radio access
network (RAN). In UMTS it is the RNC that facilitates this, in
GSM/GPRS it is the BSC, and in LTE it is the base station. The MS
is then able to take the broadcast information into account when
selecting a cell of a Routing Area and/or RAT within which to
camp.
[0051] In the idle mode, a MS continuously monitors the strengths
of the radio signals from the cells in the area. It also receives
the information broadcast regarding the support for PS handover, in
accordance with the present invention. This information provides
information about the capabilities of the cells, Routing Areas and
RATS (whether they are operated by the same or different RANs).
Thus, an indication of support by a cell or Routing Area or RAT for
a packet switched handover procedure, enables the MS to
preferentially select to camp in a cell of that particular Routing
Area and/or RAT.
[0052] Referring again to FIG. 2, the upper two RANs, which
supports PS handover, will broadcast this capability. Each RAN is
configured as a number of Routing Areas, each of which comprise of
a number of individual cells. PS handover may or may not be
supported within a cell, although typically all cells within the
same Routing Area (and possibly RAT) will share the same profile,
i.e. they will all support PS handover or they will not. If the MS
is likely to be used for VoIP calls, it can use the broadcast
information to enable it to select to camp in a cell of a Routing
Area and/or RAT which comprises cells that support PS handover. If
possible (i.e. if the RAN broadcasts the necessary network-wide
information), the MS will select to camp in a cell of a Routing
Area and/or RAT within a RAN which supports PS handover across its
network, thereby eliminating problem of bad quality of Service--for
example clips--when passing cell boundaries. By way of
illustration, a MS roaming abroad may have a choice of several
network providers. If one provider advertises that it is able to
support PS handover across its entire network whilst another
supports it only within the routing area within which the MS is
currently located, the MS may select that network provides full
coverage.
[0053] In order to avoid changes in existing RANs (BSS and UTRAN),
the absence of a PS handover support indication is interpreted to
mean that PS handover is not supported.
[0054] The present invention also allows for additional cell
capabilities to be broadcast in order to enable the MS to choose
the most appropriate Routing Area within which to camp. Thus,
static information, i.e. relating to the physical capabilities of
the cells, may be broadcast. Some examples of such information are:
[0055] Supported Quality of Service (QoS). [0056] Supported Traffic
classes. [0057] e.g. Conversational Real Time (RT), Streaming RT,
Interactive and/or Background Information. [0058] Peak throughput
(e.g. in kbits/s) for each of the supported QoS/Traffic Classes
e.g. Conversational RT is supported up to 32 kbits/s in a symmetric
way. [0059] Other relevant attributes for the different supported
QoS/Traffic classes. [0060] Current traffic load: this will change
dynamically over time depending on current traffic in a cell,
Routing Area and/or RAT. [0061] Standardized Profiles which are
supported. [0062] This feature will simplify the cell capability
information that is required to be broadcast since specific
standard profiles can be created so that only the supported
profiles need be indicated and not each of the individual
characteristics.
[0063] It may also be possible to broadcast dynamic cell
information, i.e. relating to the resources available in a cell at
a particular point in time. One example of such information is the
Current traffic load described above.
[0064] In a particular embodiment of the present invention, the MS
is capable of determining the suitability of the available cells in
relation to information stored in the MS regarding the likely use
of the MS. Thus, for example, if the user mainly uses the streaming
service, the MS could include an algorithm to recognize that so
that it can try to camp in a Routing Area and/or RAT with cells
which support the QoS class streaming.
[0065] It will be appreciated by persons skilled in the art that
various modifications may be made to the above embodiments without
departing from the scope of the present invention. For example,
whilst the above discussion has been concerned with a 2G access
network, the invention is equally applicable to a 3G access network
and to overlapping 2G and 3G networks. The invention is also
applicable to future generation networks such as 3GPP LTE/SAE.
* * * * *